Global tags to make analysis modules more release independent ?

[IzaakWN]

At the moment, things become messy when we want to analyze new nanoAOD versions that have a different set of tau IDs.

It would be desirable to have the same analysis code that can tackle different nanoAOD versions that contain different tau IDs (e.g. DeepTau2017v2p1VSjet vs. DeepTau2017v2p5VSjet, etc.), and keep track of it by something like a global tag that selects the branches we are interested in. In this way, we can retain compatibility to different nanoAOD versions without code duplication.